For normal database access, a datamodule should contain

• Only one TIBDatabase component
  (because there is no way to construct a query using records from more than one database)
• One query object for program generated queries
• One query object per table
• One Datasource object per query object
• One Transaction object per query object (this is very important)
• No Table objects (they are very slow to search and sort)

For normal database access, a datamodule should contain

• Only one TKADaoDatabase component
  (because there is no way to construct a query using records from more than one database)
• Any number of Table objects
• One Datasource object per table object
• One table object is normally reserved for program generated queries

KADao table components work fine, they are much faster than Interbase table components.

File / New... / Data Module           (Delphi 5)
File / New    / Data Module           (Delphi 6)
File / New / Other... / Data Module   (Delphi 6)   

When KADaoDatabase1 is the first component added to a datamodule, it is automatically created first.

To control the creation order, from the menu, select

Edit / Creation Order...

Creation Order...

Project / Add to Project...

The following works fine

procedure TWebModule_AB.WebModuleCreate(Sender: TObject);
begin
  SamplesDataModule := TSamplesDataModule.create(self);
end;

Applications

• Are developed on one (or several) systems
• Formally tested on another system
• Used for actual (production) work on yet another

In general, I prefer portable code that is able to determine the appropriate path at run time - I provide an ini file for that purpose.

According to the help, it is possible to add datamodules to the Repository. Once that is done, then you can inherit from those and everything should be ok.

The only problem is that the instructions on adding datamodules to the repository are almost correct. They say

2. .. For a .. data module, right-click the item and choose Add To Repository.

2. .. For a .. data module, make sure that the datamodule (not the code) is displayed (use F12 to toggle between the 2 displays) then right-click the datamodule and choose Add To Repository.

When creating a new datamodule (in Delphi 5), select File / New... / Data Modules and be sure to select Inherit (Copy is the default) before clicking OK.

NOTE: For Delphi 6, use File / New / Other... / Data Modules

• In the pas file (unit), change the object definition line from something like

    TSamplesDataModule = class(TDataModule)
  

  to

    TSamplesDataModule = class(TBasicDataModule)
  

  and add the TBasicDataModule unit (*.pas file) to the uses clause
  (This is all that is necessary for normal inheritance)

  Also, you need to delete any existing components and methods that are common to both datamodules.

• In the dfm file (form), change only the first line from something like

  object SamplesDataModule: TSamplesDataModule
  

  to

  inherited SamplesDataModule: TSamplesDataModule
  

  (This is not covered in the help file)

• In the dpr file (project), add a line specifying where the base datamodule is

    Basic_Firebird_DataModule in '..\..\Basic_Firebird_DataModule.pas' 
       {BasicDataModule: TDataModule},
  

  (This is required to edit the derived datamodule in the IDE, and may be required to compile the project. Without it, Delphi produces an error when the project is opened. By the way, the "comment" is NOT optional - it is used by the IDE. Without it, the IDE is not able to display the DataModule "forms" for the derived DataModules.)

• Add the unit name(s) to the form's implementation section uses clause
• Add Application.CreateForm to the form's Create event

This example provides 2 text fields

• Edit1 - displays the search results
• Edit2 - contains the barcode to search for

uses
  Samples_Firebird_DataModule;

procedure TForm1.FormCreate(Sender: TObject);
begin
  Application.CreateForm(TSamplesDataModule, SamplesDataModule);

end;

procedure TForm1.Button1Click(Sender: TObject);
var
 flag : boolean;
 xx : string;
begin
  flag := SamplesDataModule.CheckBarcode(Edit2.Text);
  if flag then xx := 'true'
  else         xx := 'false';
  Edit1.Text := xx;
end;

• Delphi 5 - Forms
• Delphi 6 - Classes

  // Delphi 5 example 
uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs;

  // Delphi 6 example 
uses
  SysUtils, Classes;

{$IFDEF VER130}       // Delphi 5
  {$DEFINE mc_LE_D5}  // Less than or equal to Delphi 5 
                      // I use "mc" to help avoid conflicts
{$ENDIF}

uses
  SysUtils, Classes,
{$IFDEF mc_LE_D5}
  Forms, // Delphi 5 and below only 
{$ENDIF}
  other, units, go, here
  ;    // Don't forget the semicolon

URL: http:// cpcug.org / user / clemenzi / technical / Databases / Delphi / DataModules.html